This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Our goal is to perform studies on early intrauterine pregnancy (IUP) in rhesus macaques. During pregnancy the vessels of the endometrium are extensively modified to provide blood flow to the growing conceptus. Contrast-enhanced ultrasound (CEU) is a new technique capable of high-resolution imaging of the microvasculature within organs. The method relies on the detection of gas-filled microbubbles that are injected intravenously while imaging by ultrasound. Our hypothesis is that CEU imaging will permit earlier visualization of embryo implantation and for the first time a detailed evaluation of the growing endometrial vessels at the fetal-maternal interface. Our Specific Aim is to develop microbubble CEU for visualization of early pregnancy and assessment of intrauterine vascular parameters during embryo implantation in rhesus macaques. We have now demonstrated that CEU can identify the primary placental lobe and underlying vessels ~2 days earlier than the conventional method, Doppler Ultrasound (DUS), detected pregnancy-associated endometrial thickening. CEU revealed changes in vascular perfusion between the endometrium, myometrium, and the endometrial-myometrial junctional zone. In addition to the high rate of blood flow to the growing conceptus, CEU identified a high rate of blood flow to the myometrium (10 mL/min/g tissue), with less flow in the endometrium and endometrial-myometrial zone (3 mL/min/g) distant from the site of implantation. We conclude that CEU provides a sensitive, non-invasive method to assess vascular perfusion of the macaque uterus during embryo implantation. We propose CEU as a new diagnostic tool to monitor vascular changes associated with early pregnancy in women.